The production in mass quantities of many articles requires the filling of precise measured amounts of chemical materials in powdered or granular form. For instance, in the dispensing of drugs, it is very important to weigh out into each vial or container precise amounts of the material for each tablet or capsule. Indeed, the standard practice in the drug industry is to volumetrically control the amount of material making up each tablet or capsule, since conventional weighing units have been found to be either too slow or inaccurate. It is therefore essential in the production of drugs in mass quantities to provide a high speed system for weighing out each dose and, once weighed, to advance or remove each dose into another receptacle, such as, a vial or container for packaging same. As will become more apparent, the present invention is by no means limited in application to the dispensing of medicines, drugs, or other chemical materials for that matter; however, its novel features and characteristics may be best understood and appreciated from a consideration of its use in that area.
In the past, weighing and filling systems have been devised for dispensing selected amounts of comminuted materials. For example, U.S. Letters Patent to Smith U.S. Pat. No. 1,364,003 discloses a grain receiver used in combination with a hopper which is solenoid-operated to dispense materials. Another patent of interest is to Schrock U.S. Pat. No. 2,625,361 which discloses a weighing and filling device having a material receiver and dumping mechanism which is tilted from side to side to dump the material. U.S. Pat. No. 4,261,485 to Borg is directed to a magnetically operated valve having magnets which slide under the influence of gravity relative to one another so as to repel a permanent magnet-bearing plunger either to an open or closed position. U.S. Pat. No. 2,609,974 to Brous discloses a valve which is selectively opened or closed by a magnetically actuated plunger. Other prior art of general interest in the field of weighing and filling are U.S. Pat. Nos. 3,974,941 and 4,262,824 to Mettler and Hrynewycz.
The prior art as exemplified by the aforementioned patents is considered to fall short in achieving the necessary speed and accuracy in the successive weighing out of selected amounts of material and in such a way as to avoid waste, inaccurate fillings, and greatly reducing the cost of the production of articles requiring such materials where such articles are to be produced in mass production operations. Although conventional apparatus may be adequate to meet establishing weighing tolerances for weighing out relatively large quantities of material, they have not been found to be capable of accurately and rapidly weighing and filling in the lower weight ranges, such as, on the order of 0.10 lbs. to 0.0001 lbs. and where the fill rates must be as high as 10 to 600 fills per minute.